I almost failed to locate the immigration to the United States of a widowed ancestor. Nanke Albers Bruns "hopped on the boat" when her last child immigrated to the United States in the 1860s. I had not thought to even look for her and there she was, listed on the same manifest with her son (my uncle).
If I hadn't bothered to look for the son, I might not have found her.
One more reason to look for those siblings, even when you think you don't need to.